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# Compare the process of calcination and roasting.

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## The comparison between calcination and roasting is as follows: Calcination Roasting 1. The process of heating a concentrated ore in the absence of air is called calcination. The process of heating a concentrated ore in the presence of air is called roasting. 2. Generally, hydrated oxide and carbonate ores are calcined. Generally, sulphide ores are roasted. 3. During calcination, hydrated oxide and carbonate ores are converted to metallic oxides. E.g.${\mathrm{ZnCO}}_{3}\stackrel{\mathrm{Calcination}}{\to }\mathrm{ZnO}+{\mathrm{CO}}_{2}\phantom{\rule{0ex}{0ex}}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}.2{\mathrm{H}}_{2}\mathrm{O}\stackrel{\mathrm{Calcination}}{\to }{\mathrm{Al}}_{2}{\mathrm{O}}_{3}+2{\mathrm{H}}_{2}\mathrm{O}$ During roasting, sulphide ores are converted to metallic oxides or metallic sulphates or into metals. E.g.$4{\mathrm{FeS}}_{2}+11{\mathrm{O}}_{2}\stackrel{\mathrm{Roasting}}{\to }2{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}+8{\mathrm{SO}}_{2}\phantom{\rule{0ex}{0ex}}2\mathrm{ZnS}+3{\mathrm{O}}_{2}\stackrel{\mathrm{Roasting}}{\to }2\mathrm{ZnO}+2{\mathrm{SO}}_{2}$ 4. Calcination removes moisture, volatile impurities and any organic matter present in the ore. It makes the ore porous. Roasting removes moisture, volatile impurities of P, As and S (escapes in the form of gases) ores. It makes the ore porous. 5. Calcination is carried out in a reverberatory furnace by keeping the holes in the furnace closed. Roasting is carried out in a reverberatory furnace by keeping the holes in the furnace open, so as to allow air to enter the furnace.

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